The present invention relates to apparatus for treating liquids at elevated temperatures by introduction of substances thereto. Treatment may be performed on the liquid while in a vessel of some kind or while flowing along a conduit or channel.
Liquids to be treated will ordinarily be at such high temperatures that they may be regarded as aggressive or dangerous. The apparatus we have developed has been designed to be safe in operation as well as adequately protected from the liquid up to the time treatment is to begin.
Exemplary liquids for treatment include molten slags and metals. Regarding metals, both ferrous and non-ferrous melts may be treated for diverse purposes using the present apparatus. Apparatus to be described has been designed principally, but not exclusively, for introducing gases, powders and solids to ferrous melts.
The apparatus could also be used in winning or refining selected metals from their ores. For example, tungsten can be won by reduction in an arc furnace of the ore or an oxide thereof to the molten metallic state. The present apparatus can be employed to blow fresh powdered ore or oxide into the metallic melt of the furnace.
The apparatus disclosed hereinafter in detail can be employed when making steel from iron. It is suitable for use in vacuum degassing as a convenient means to introduce alloying additions. Primary and secondary refining, deoxidizing and desulphurizing can be performed to advantage with the aid of the apparatus. Compositions of steels (and other metals) can be controlled or modified by introducing gaseous, solid or powdered substances at any time before solidification. For instance, the melt can be treated in the furnace, in the ingot mould, as well as in vessels such as steelmaking vessels, ladles of various kinds, degassers and tundishes.
Before or during teeming in a metal casting operation, it may be necessary or desirable to introduce gas into the molten metal in a container or vessel. Gas is injected, e.g. into the bottom area of a vessel, for diverse purposes. These include rinsing; clearing the relatively cool bottom area of solidification products, to help remove them from the vicinity of a vessel bottom outlet from which the metal may be teemed; equalising the temperature throughout the melt; and stirring to help disperse alloying additions uniformly in the melt. Usually an inert gas such as argon is used. Reactive gases such as oxygen, carbon dioxide and hydrocarbon gases are sometimes substituted, depending on the melt chemistry.
Previous gas injection proposals have envisaged porous bricks in the refractory lining of a vessel, solid porous plugs in sliding gate teeming valves, and conventional consumable lances. Installations featuring porous bricks have the virtue of simplicity. Unfortunately, a porous brick exposed to the interior of the vessel may be rendered inoperative if metal slags or metal oxides freeze on it, e.g. between emptying the vessel and refilling it. Moreover, when refilling, these bricks could be damaged through impact of the molten metal thereon or through thermal shock. Unexpected failure of the brick can have extremely dangerous consequences. Visual inspection to detect the onset of failure is far from easy from a distance, looking down into the vessel.
Sliding gate valves adapted for gas injection may be safer, but unless overly complicated they are not able to offer the possibility of gas injection simultaneously with teeming.
Conventional lances are somewhat cumbersome, costly and not without their dangers in view of the splashing their use engenders.
Among other things, the present invention aims to overcome the above drawbacks associated with prior gas injection systems. The apparatus disclosed hereinafter is capable of introducing substances deep into a metal melt and provides benefits not so readily attainable by the consumable lances conventionally employed.
In ferrous metallurgy, the melt must often be deoxidised and desulphurised by introducing aluminium and calcium or its alloys. Composition control or "trimming" is commonly performed by dissolving solid or powdered alloying additions in the melt. Many materials can be added to melts to overcome the deleterious effects of impurities or to tailor the melts to produce specified compositions. We do not propose to provide an exhaustive catalogue of possible treatment materials. The choice of materials will depend on the melts, their starting and finishing compositions; it is well within the purview of the works chemist or metallurgist to choose appropriate addition(s) as each situation demands. Introducing additions to a steel melt--or indeed any other metal melt--can be troublesome especially if the alloying addition is readily melted, oxidised or vaporised. Thus, adding aluminium to a steel melt can be a difficult operation in view of the low melting point of aluminium. No significant deoxidation would be achieved if the aluminium were simply dumped onto the melt: it has to be delivered deep into the melt so it has time to liquify and react rather than float ineffectively on top of the melt. Calcium moieties have to be fed deep into the melt. Previous delivery methods include use of a lance or sophisticated and expensive equipment for firing the alloying addition deep into the melt. Lancing is apparently simple but has drawbacks as intimated above.
The apparatus disclosed hereinafter facilitates the introduction of alloying or treatment additions in powder or solid form deep into a metal melt. By means of this apparatus, precise dosing of the melt is a very straightforward operation. In its preferred form, inert or reactive gases can be blown into the melt in the course of introducing powders or solids.